*{
    margin: 0;
    padding: 0;
}
body{
    text-align: center;
}
#list{
    margin: 100px auto;
    border: 1px solid #fff;
    border-left: none;
    border-top: none;
    overflow: hidden;
    background: url('/spiral/img/bg.jpg') 0 0 no-repeat;
    background-size:cover; 
}
#list li{
    list-style: none;
    float: left;
    border: 1px solid #fff;
    border-right:none;
    border-bottom: none;
    box-sizing: border-box;
    background-size:cover; 
}
#list li.active{
    animation: flash .5s linear infinite;
}
@keyframes flash {
    0%{
        opacity: 0.1;
    }
    50%{
        opacity: 1;
    }
    100%{
        opacity: 0.1;
    }
}